It is well known in the art to utilize a CMM to measure objects in a space in terms of their X, Y, and Z coordinates commonly referring to length, width and height. Advancement in the art has led to lightweight portable CMM's well suited for general industrial applications. Such a CMM is disclosed in U.S. Pat. No. 5,402,582 which is commonly assigned to the assignee hereof and incorporated herein by reference. Three dimensional objects are described in terms of position and orientation; that is, not just where an object is but in what direction it points. The orientation of an object in space can be defined by the position of three points on the object. Orientation can also be described by the angles of alignment of the object in space. The X, Y, and Z coordinates can be most simply measured by three linear scales. In other words, if you lay a scale along the length, width and height of a space, you can measure the position of a point in the space.
Presently, coordinate measurement machines or CMM's measure objects in a space using three linear scales. Coordinate measuring machines of the prior art comprise a multijointed (preferably six joints) manually positional measuring arm for accurately and easily measuring a volume which typically comprises a sphere preferably ranging from six to eight feet in diameter (but which may also cover diameters more or less than this range). In addition to the measuring arm CMM's of the prior art employ a controller (or serial box) which acts as the electronic interface between the arm and a host computer which displays menu prompts and outputs to an operator. The mechanical measuring arm used in CMM's generally comprise a plurality of transfer housings (with each transfer housing comprising a joint and defining one degree of rotational freedom) and extension members attached to each other with adjacent transfer housings being disposed at right angles to define a movable arm preferably having five or six degrees of freedom. Each transfer housing includes measurement transducers. In addition, each transfer casing includes visual and audio endstop indicators to protect against mechanical overload due to mechanical stressing.
The use of a discrete microprocessor-based controller box permits preprocessing of specific calculations without host level processing requirements. This is accomplished by mounting an intelligent preprocessor in the controller box which provides programmable adaptability and compatibility with a variety of external hosts (e.g., external computers). The serial box also provides intelligent multi-protocol evaluation and auto switching by sensing communication requirements from the host. For example, a host computer running software from one manufacturer will generate call requests of one form which are automatically sensed by the controller box. Still other features of the controller box include serial port communications for standardized long distance communications in a variety of industrial environments and analog-to-digital/digital counter boards for simultaneous capture of encoder data from all of the transfer housing resulting in highly accurate measurements.
CMM's of the prior art include transducers (e.g., one transducer for each degree of freedom) which gather rotational positioning data and forward this basic data to a serial box. The serial box provides certain preliminary data manipulations. In a typical configuration the serial box is positioned under the host computer somewhat remotely from the probe and of the arm. The serial box includes EE-PROMS which contain data handling software, a microcomputer processor, a signal processing board and a number of indicator lights and audio output, usually in the form of a speaker. As mentioned, basic transducer data is sent from the arm to serial box where the serial box then processes the raw transducer data on an ongoing basis and responds to the queries of the host computer with the desired three dimensional positional or orientational information.
Presently CMM systems require that the operator, while manipulating the arm, refer back to the display screen of the host computer and respond to alphanumeric messages displayed thereon or respond to audio signals. The messages and audio signals are generated by the host computer and applications software. In certain cases the components of the CMM system (e.g., the arm, serial box and host computer with display) are arranged in positions which are often difficult or inconvenient for the operator to see or hear.
Measurement arms for CMM's include a probe handle at the operator end. Probe handles of the prior art are held by an operator as either a pencil or pistol grip and sometimes possess two switches for the attachment of optional electronics and/or a threaded mount for receiving a variety of probes. Because the CMM is a manual measurement device, the user must be capable of taking a measurement and then confirming to CMM whether the measurement is acceptable or not. This is typically accomplished through the use of the two switches. One switch is used to trap the 3 dimensional data information and the second switch confirms its acceptance and transmits it to the host computer. A number of voltage lines and analog-to-digital converter lines are routed from the serial box through the arm to the probe handle for general attachment to a number of options such as a laser scanning device or touch probe. The switches are also used to respond to menu prompts, either displayed or audio signals, from the host computer.
A variety of probes may be threaded to a probe handle assembly such as a hard 1/4 inch diameter ball probe or a point probe is shown. The probes are typically threadably mounted to mount which in turn, is threadably mounted to a probe housing and may also include a plurality of flat surfaces for facilitating engagement and disengagement of the probes using a wrench.
The front panel of a serial box of the prior art has eight lights including power indicator light and error condition light and six other lights corresponding to each of the six transducers located in each transfer housing. Upon powering up, the power light will indicate power to the arm. The six transducer lights indicate the status of each of the six transducers.
The status lights may indicate, for example, if any of the transducers approach its rotational endstop from within 2 degrees, the light, and an audible beep, for that particular transducer indicates to the user that the user is too close to the end stop; and that the orientation of the arm should be readjusted for the current measurement. The serial box will continue to measure but will not permit the trapping of the data until such endstop condition is removed. A typical situation where this endstop feature is necessary is the loss of a degree of freedom by the rotation of a particular transducer to its endstop limit and, hence, the applications of forces on the arm causing unmeasured deflections and inaccuracies in the measurement.
At any time during the measurement process, a variety of communication and calculation errors may occur. These are communicated to the user by a flashing of the error light and then a combination of lights of the six transducers indicating by code the particular error condition. Some serial box front panels utilize an alphanumeric LCD panel giving alphanumeric error and endstop warnings.